php try catch : 捕捉异常,抛出异常

/**     
* 构造函数：自动加载连接数据库     
* @param  $database  $key     
* @return       
*/    
private function __construct($database = array(), $key){
        try{
            $this->server = $database['db_host'];            
            $this->username = $database['db_user'];            
            $this->password = $database['db_pwd'];            
            $this->database_name = $database['db_name'];            
            $this->database_type = $database['db_type'];            
            $this->database_port = $database['db_port'];            
            if($this->database_type == 'mysql'){                
            $this->pdo = new PDO($this->database_type . ':host=' . 
            $this->server . ';port=' . 
            $this->database_port                     . ';dbname=' . 
            $this->database_name, 
            $this->username,
            $this->password, array(PDO::ATTR_TIMEOUT => self::TIME_OUT));            
            }else{            
            $this->pdo = new PDO ("dblib:host=$this->server:$this->database_port;
            dbname=$this->database_name","$this->username","$this->password");            
            }            
            $this->pdo->exec('SET NAMES \'' . $this->charset . '\'');            
            self::$pdo_ref[$key] = &$this->pdo;                       
            }catch(PDOException $e){            
            echo $e->getMessage();        
            }    
            }